Name__________________________________________ Period____________ Date________________
SOME GO “POP,” SOME DO NOT
Volcanic eruptions can range from mild to violent. When volcanoes erupt, the materials left behind provide information
to scientists studying the Earth’s crust. Mild, or non-explosive, eruptions produce thin, runny lava that is low in silica.
During non-explosive eruptions, lava simply flows down the side of the volcano. Explosive eruptions, on the other hand,
do not produce much lava. Instead, the explosions hurl ash and debris into the air. The materials left behind are light in
color and high in silica. These materials help geologists determine the composition of the crust underneath the
volcanoes.
Volcano Name
Alcedo
Coordinates
26°S 91°W
Niuafo’ou
15°S 175°W
Mount St. Helens
46°N 122°W
Kilauea
19°N 155°W
Pavlof
55°N 161°W
Popocatépetl
19°N 98°W
Soufriere Hills
16°N 62°W
Long Valley Caldera
37°N 119°W
Okmok
53°N 168°W
Rabaul caldera
4°S 152°E
Fernandina
42°N 12°E
Mount Pinatubo
15°N 120°E
Description
Type of Eruptions
The Alcedo volcano in the Galapagos last
erupted in 1993 with flows of basaltic lava.
Niuafo’ou has been volcanically active for
thousands of years. Lava flows from an
eruption in 1912 and 1929 destroyed the
village of Futu.
An explosive eruption blew the top off of
the mountain. Light-colored ash covered
thousands of square kilometers. Another
eruption sent a lava flow down the
southeast side of the mountain.
One small eruption sent a lava flow along
12km of highway.
Eruption clouds have been sent 200m
above the summit. Eruptions have sent
ash columns 10km into the air.
Occasionally, small eruptions have caused
lava flows.
During one eruption, Mexico City closed
the airport for 14 hours because huge
columns of ash made it too difficult for
pilots to see. Eruptions from this volcano
have also caused damaging avalanches.
Small eruptions have sent lava flows down
the hills. Other explosive eruptions have
sent large columns of ash into the air.
Explosive Eruptions have sent ash into the
air.
Recently, there have been slow lava flows
from this volcano. Twenty-five hundred
years ago, ash and debris exploded from
the top of this volcano.
Explosive eruptions have caused tsunamis
and have left 1-2m of ash on nearby
buildings.
Eruptions have ejected large blocks of rock
from this volcano.
Ash and debris from an explosive eruption
destroyed homes, crops, and roads within
52,000km² around the volcano.
Analysis Questions:
1) According to your map, where are volcanoes that always have non-explosive eruptions usually located?
2) Where are volcanoes that always erupt explosively usually located?
3) Where are volcanoes that erupt both ways usually located?
4) If volcanoes get their magma from the crust below them, what can you say about the silica content of Earth’s
crust under the oceans?
5) What is the composition of the crust under the continents? How do we know?
6) What is the source of materials for volcanoes that erupt in both ways? How do you know?